Apparatus and method for compensating for errors in temperature measurement of semiconductor wafers during rapid thermal processing

ABSTRACT

The present invention is an apparatus for calibrating a temperature feedback value in a water processing chamber to automatically compensate for variations in infrared emissions from a heated semiconductor wafer due to variations in composition and coatings from wafer to wafer. A calibration wafer with an imbedded thermocouple is used to generate a table relating actual wafer temperatures to power supplied to the heating chamber and infrared emissions detected by a pyrometer. A sample wafer of a batch to be processed is subsequently placed in the chamber at a known power level, and any difference between the detected infrared emission value and the value in the table is used to adjust the entire table according to a first predetermined formula or table. Before each wafer is processed, a known source of infrared light is reflected off the wafer and detected. The reflected light value is compared to a reflection measurement for the sample wafer. The difference in reflection measurements is correlated to emissions from heating, and the calibration table is fine-tuned with the correlation value according to a second predetermined formula or table to account for variations in emissions between individual wafers due to variances in wafer surface conditions.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for calibratinga light emission measurement heating chamber to automatically compensatefor varying backside conditions on a semiconductor wafer.

Recently, there has been a trend toward single wafer processing ofsemiconductor wafers, rather than batch processing. Single waferprocessing ensures that the processing of each wafer is more precise andthat there is a higher level of consistency between wafers Therefore,when the wafer is transformed into its final form, it functions morepredictably and more accurately. As increasing densities of componentson wafers are developed, the need for very precise processing increases.In order to achieve throughputs similar to conventional wafer ovenswhich process a large number of wafers at once, a rapidly heating arclamp is used, instead of a heating element, to speed up the processingtime.

Apparatus for rapid thermal processing of semiconductor wafers are knownin the prior art For example, U.S. Pat. No. 4,755,654 (hereinafter '654)discloses a semiconductor wafer heating chamber for applying either adesired uniform or non-uniform heating pattern to a wafer. The apparatusof '654 includes a long-arc AC gas-discharge lamp with a spectral outputtuned for absorption by silicon. The lamp is capable of quickly raisingthe temperature of the wafer to a desired process temperature andholding it there for the time period necessary to accomplish thespecific step of the process. Since the lamp heats the wafer quickly,the apparatus of '654 can be used efficiently to process wafers one at atime. The lamp heats the wafer with light directed to the top, or frontside, of the wafer. A pyrometer is used to detect the infrared lightemitted from the backside of the wafer when it is heated. This light isproportional to the temperature of the wafer. The pyrometer output isprovided as a feedback to the heating system.

A pyrometer works by measuring the amount of radiation emitted in acertain spectral band (or bands) from the object to be measured. Allobjects emit radiation if they are at any temperature above absolutezero. The emitted radiation can be described quantitatively in a verysimple form by the Stefan-Boltzmann Law. The radiant energy equals theemissivity times the Stefan Boltzmann constant times the temperature tothe fourth power.

The spectral content of this radiation can also be determined usingPlank's Law. Since one can calculate the amount of radiation emitted andthe spectral distribution of the radiation, it should be simple tomeasure the radiation and work backwards to calculate the temperature.This would be true except that the factor "emissivity" is not, in mostcases, a known constant. In fact, it is usually not a constant at all,but a function of wavelength and temperature. Therefore, to usepyrometry to accurately measure temperature, one must calibrate thesystem by effectively measuring "emissivity".

The calibration of the pyrometer feedback value indicating thetemperature of the heating chamber is critical in the processing of aparticular wafer. Presently, calibration of pyrometers used in waferprocessing ovens is accomplished manually. The pyrometer is exposed to alight of a known value and the gain of the pyrometer output is adjustedto the desired value for such value of light using a potentiometer.

SUMMARY OF THE INVENTION

The present invention is a method and apparatus for calibrating atemperature feedback value in a wafer processing chamber toautomatically compensate for variations in infrared emissions from aheated semiconductor wafer due to variations in composition and coatingsfrom wafer to wafer. A calibration wafer with an imbedded thermocoupleis used to generate a table relating actual wafer temperatures to powersupplied to the heating chamber and infrared emissions detected by apyrometer. A sample wafer of a batch to be processed is subsequentlyplaced in the chamber at a known power level, and any difference betweenthe detected infrared emission value and the value in the table is usedto adjust the entire table according to a first predetermined formula ortable. Before each wafer is processed, a known source of infrared lightis reflected off the wafer and detected. The reflected light value iscompared to a reflection measurement for the sample wafer. Thedifference in reflection measurements is correlated to emissions fromheating, and the calibration table is fine-tuned with the correlationvalue according to a second predetermined formula or table to accountfor variations in emissions between individual wafers due to variancesin wafer surface conditions.

In a preferred embodiment, the apparatus includes two pyrometers. Thefirst pyrometer is located in a reflection chamber adjacent to theheating chamber where a reflectivity test is performed on wafers beforethey are placed in the heating chamber. A black body radiation source ismounted adjacent to the first pyrometer in the reflection chamber andprovides infrared light aimed at the wafer. The infrared light which isreflected off of the wafer is measured by the first pyrometer.

A second pyrometer is used to detect the amount of infrared lightemitted by a wafer during heat processing in the processing chamber. The"frontside" , or top, of the wafer is illuminated and heated by an arclamp near the top of the chamber. The second pyrometer, mounted at thebottom of the chamber, detects infrared emissions from the "backside" ,or bottom, of the wafer. A computer has inputs connected to the twopyrometers and an output which controls the power source of theprocessing chamber.

The operation of the present invention to perform precise calibration iscarried out in a series of steps. First, a thermocouple wafer isintroduced into the processing chamber. A thermocouple wafer is asemiconductor wafer provided with an imbedded thermocouple to detect iscore temperature. It is used for calibration purposes only and is notprocessed. A series of known power levels are applied to the heatingelement of the processing chamber and the resulting temperature andamount of light emitted by the wafer at each power level is recorded ina calibration table.

A second wafer without a thermocouple device is then introduced into theprocessing chamber. The second wafer is a "batch" wafer withrepresentative backside characteristics from a particular batch ofwafers. A particular power level with a corresponding known temperature(from the set of values applied to the thermocouple wafer) is applied tothe second wafer. The corresponding light emission value for theparticular power level for the second wafer is detected. The differencebetween this value and the corresponding value for the thermocouplewafer is noted. This difference is used to revise the light emissionvalues in the calibration table to produce a new, batch-specificcalibration table.

Preferably, the front side of the second wafer is stripped, so that anycoatings or surface conditions do not affect the amount of lightabsorbed, and thus the temperature achieved, for a given lightintensity. Alternatively, an error factor can be built in to account forless or more light being absorbed resulting in too low or too high atemperature for the energy emitted.

Optinally the second batch wafer may be introduced into the reflectivitychamber to obtain greater accuracy in some cases. The black bodyradiation source is activated to provide infrared light which isreflected off of the wafer. The amount of light reflected is measured bythe first pyrometer. The reflected light value is stored in memory. Eachwafer to be processed is passed through the reflectivity chamber, and asimilar measurement is done. The difference between the reflectivitymeasurement for a current wafer and the second, batch wafer iscalculated. This difference is converted to an emissivity correctionfactor for each emissivity value and is used to revise the batchspecific calibration table to produce a new, wafer specific calibrationtable. This wafer specific table will be used by the computer to adjustthe pyrometer feedback value for any desired processing. Each wafer tobe processed will have a separate wafer specific calibration table.Alternatively, the batch wafer temperature measurement could be omitted,with only the thermocouple wafer and reflectivity measurements beingdone.

The precise calibration is completed automatically so that there is noroom for operator error. The computer makes all the data manipulationsand sets the heating chamber for processing according to the informationprovided. The calibration for a batch of wafers is fast because only asingle measurement for a single temperature is needed to adjust theentire table. The reflection measurement for individual wafers is evenfaster, since there is no need to wait for the oven to heat.Additionally, the calibration technique is fast because it is carriedout by the computer. There is no need for manual adjustments.

The advantages achieved by the use of the calibration apparatus andmethod are numerous. First, the consistency of operation between wafersof similar composition is increased. This is because each wafer isprecisely processed according to its own particular characteristicsdemonstrated before processing. By taking the particular characteristicsof the wafer into account during processing, the final form of eachwafer more closely approaches that of any other processed wafer.

For a more complete understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the arrangement of the components ofthe caIibration apparatus according to a preferred embodiment of thepresent invention;

FIG. 2 is an illustration of the thermocouple wafer used to obtaininitial semiconductor wafer characteristics according to a preferredembodiment of the present invention;

FIG. 3 is a chart of the pyrometer voltage level versus temperature ofparticular wafer measured by a preferred embodiment of the presentinvention;

FIG. 4 is a block diagram of the electronics used to implement apreferred embodiment of the present invention; and

FIG. 5 is a flowchart of the software used to control the computer in apreferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Overall SystemStructure

FIG. 1 is a diagram showing the arrangement of the components of thecalibration system in a preferred embodiment. A reflection chamber 10includes a wafer platform 12 upon which a wafer 14 is placed during areflectivity test. A black body radiation source 16 provides infraredlight to be reflected off of a backside 18 of wafer 14. A firstpyrometer 20 mounted adjacent to black body radiation source 16 detectsthe amount of light reflected off of backside 18 of wafer 14.

The calibration system contains a processing chamber 30 for processingwafers A transfer arm 21 is used to swing wafer 14 from reflectionchamber 10 to processing chamber 30 in a loading operation. A lamp 32 issituated inside chamber 30 and above wafer 14. The wafer is seated on awafer platform 34, similar to wafer platform 12 in reflection chamber10. Below wafer platform 34 is a second pyrometer 36 for detecting theamount of light emitted by wafer 14 during processing.

First and second pyrometers 20, 36 have output lines 40, 42 connected toa computer 44. In addition, an output 46 indicating the power level of apower supply 47 of processing chamber 30 is connected to computer 44Each of these output lines 40, 42, 46 provide computer 44 with data forsetting the processing chamber for the characteristics of a particularwafer. A computer output line 48 is connected to a control input forpower supply 47 so that computer 44 may set lamp 32 at the proper levelfor processing. Computer 44 is provided with a keyboard 50 and a display52 so that a user may interact with the system to access and input data.

System Operation

The operation of the present invention will now be described withreference to FIG. 1. Calibration of the processing system for processingsemiconductor wafers is carried out in a series of three steps conductedon three different wafers.

1. Thermocouple Calibration

First, a thermocouple wafer 60 is placed on wafer platform 34 inprocessing chamber 30. FIG. 2 shows a thermocouple wafer 60 used forcalibrating the system to a rough initial level. Thermocouple wafer 60includes an imbedded thermocouple 62 located at the core of thermocouplewafer 60 for detecting the core temperature of thermocouple wafer 60 asthe temperature of processing chamber 30 is increased. A high meltingtemperature thermocouple (such as Type C* - tungsten tungsten/rhenium)is preferably electron beam welded directly into the silicon wafer(rather than inserting a thermocouple into a hole in the wafer).

In this configuration, the wafer is mechanically very rugged and willsurvive many thermal cycles. The thermocouple junction is in intimatethermal contact with the wafer so the thermocouple temperature readoutwill be the same as the wafer temperature. Another advantage of thissystem is the lack of any foreign material on the wafer surface whichwould modify the coupling of radiation into the wafer. Finally,thermocouples can be added to any type of silicon wafer not just a bareone. This will be important in the overall calibration scheme.Additionally, this calibration technique is applicable to materialsother than silicon, e.g., GaAs, InP, InSb, etc.

A known power level is supplied to lamp 32, thereby heating thermocouplewafer 60 to a certain temperature. That temperature is detected bythermocouple 62. This data is then transmitted to computer 44 where thetemperature is recorded in a first table in the memory of computer 44.

In addition, second pyrometer 36 detects the amount of light emitted bythermocouple wafer 60 at the known power level. This value is stored,along with the known power level and the corresponding temperature inthe first table in the memory of computer 44.

The temperature of thermocouple wafer 60 is then increased a number oftimes. At each level the temperature and the corresponding lightemission value are recorded in the first table. This table represents aninitial rough calibration scale for semiconductor devices of similarcomposition to thermocouple wafer 60. Refinement of the values in thefirst table are accomplished by conducting tests (steps 2 and 3described below) on a batch wafer and then a particular wafer to beprocessed.

The emissivity of silicon (ignoring surface or spectral effects) isrelatively constant at temperatures above about 700° C, so emissivitycalibration as a function of temperature is not strictly required if allprocesses are to run in a restricted temperature range and small (10-20°C) temperature errors can be tolerated. In practice, the system takesmeasurements at very small temperature increments at low temperatureswhere the emissivity is changing rapidly, and at larger steps at highertemperatures.

FIG. 3 is a chart of the calibration table values for the pyrometeroutput voltage versus temperature of a particular wafer measured by apreferred embodiment of the present invention. The vertical axisrepresents the pyrometer voltage level in millivolts. The horizontalaxis represents the temperature in ° C.

Four curves are illustrated in FIG. 3 Curve 92 represents the pyrometervoltage versus temperature function of thermocouple wafer 60 at thelower end of the temperature range, i.e. 350-600° C. Curve 94 representsthe pyrometer voltage versus temperature function of the samethermocouple wafer at a higher temperature range, i.e. 500-1275° C. Thereason that two separate curves exist for the same wafer over the fullange of temperatures between 350 and 1275° C is that the pyrometer isswitched to a higher gain at about 550° C. This causes a new curve to bestarted at a lower voltage level. Curves 96 and 98 reflect theadjustments done for the sample batch wafer and a particular individuaIwafer, respectively, at the high gain setting, as discussed later,similar curves are produced for the lower voltage range, but are notshown.

2. Rapid Reference

The second step, referred to as the rapid reference, consists ofmeasuring characteristics of a batch wafer and creating an autocalcalibration file for the pyrometer that is specific to thosecharacteristics. A batch wafer is an arbitrary wafer selected from abatch of wafers of a particular lot which are to be processed. Theautocal file is created by adjusting a file for the thermocouple wafersor another known good autocal file that is in the computer memory. Thegood autocal file is selected and is known as the source file. The batchwafer is placed on wafer platform 34 in processing chamber 30. The lampis powered to one of the known power levels used in the first stepdescribed above (Power level A). Then, second pyrometer 36 detects thelight emitted by the batch wafer P(mv) and transmits it to computer 44on second pyrometer output line 42.

The computer then determines a temperature from the source autocal filethat corresponds to P(mv) and calculates the difference in temperaturebetween the indicated and the rapid reference calibration temperaturethat was measured during the thermocouple wafer calibration. Thecomputer also corrects for variations in the pyrometer gain from systemto system by determining the correction coefficient, C_(i) thatcorresponds to the particular P(mv) from the empirically derived formulaC_(i) =A_(o) +A_(i) *P_(i) (mv). The numerical value of the coefficientsA_(o) and A_(i) depend on the gain of the output amplifiers of thesecond pyrometer. The values of C_(i) for each pyrometer output valueP_(i) have been previously determined in a calibration of the particularhardware. This calibration is done by plotting the temperature of agroup of wafers for the same pyrometer output versus the reflectivity ofthose wafers. This is repeated over the range of pyrometer outputs. Theequation describing the curve formed by this plot is A_(o) +A_(i) *P_(i)(mv). By determining the values A_(o) and A_(i) , only these two valuesneed to be stored, with C_(i) being calculated each time for a pyrometerreading P_(i). Alternately, values of C_(i) could be stored in memoryfor each P_(i). There are functionally similar equations that providethe correction coefficients for both the high and low tables in theautocal file.

Using the temperature difference, ΔT, and the Correction Coefficient,C_(i), the computer calculates a Correction Constant, D. Using thisCorrection Constant each of the 256 temperatures in the high and lowtables of the autocal file are corrected according to equation

D is determined from the equation

    D=ΔT/C.sub.1.

    Tnew.sub.i =T.sub.i +D*C.sub.i                             (1)

Where:

Tnew₁ =new temperature value for the table in the ith position

T_(i) =temperature value from the source autocal file in the ithposition

D= the Correction Constant calculated from the difference between theindicated and actual temperature

C₁ =the Correction Coefficient corresponding to the ith position in theautocal table

The newly calculated values are stored in a second table. The secondtable is a copy of the first table wherein the newly calculated valuesfor light emission and temperature for the batch wafer are substitutedfor the values recorded for thermocouple wafer 60.

Curve 96 in FIG. 3 plots the values from the table for the batch wafer.Curve 96 represents a refinement of curve 94 based on measurements takenfrom the batch wafer. However, unlike curves 92 and 94, curve 96 is nota curve of actually measured values. Instead, curve 96 is anapproximated curve determined by taking a single light emission readingfrom the batch wafer at a known power level A. The power level A andlight emission value for the batch wafer are then used to predict acurve 96 for the batch wafer based on the measurements from curve 94 ofthe thermocouple wafer.

Rapid Reference works best at temperatures where emissivity is fairlyconstant, so 800° C. is normally chosen as the expected temperature (theknown power level A). For process such as TiSi₂ and A1 alIoying whichrequire lower temperatures, lower power levels can be used. It isimportant to remember that for Rapid Reference to work accurately, thefront side 19 of the wafer must be stripped. Otherwise, the differencesin the way the heat source couples into the wafer will drive the wafersto different equilibrium temperatures. Front side coupling and backsideemissivity are related physical processes but must be consideredindependently in this case because of the different spectral ranges usedfor the heat source and pyrometer.

3. Automatically Compensate Emissivity (ACE˜)

To obtain greater accuracy in some cases, step three, ACE, is performedwhich involves a reflectivity test performed on a particular wafer to beprocessed. Wafer 14 is placed on wafer platform 12 in reflection chamber10. Black body source 16 provides an infrared light aimed at backside 18of wafer 14. The amount of light reflected off of backside 18 isdetected by first pyrometer 20. This value is transmitted to computer44. This measurement is first done for the batch wafer of step 2(autocal) or for the thermocouple wafer of step 1 and then for eachindividual wafer as it is loaded for processing.

The computer first determines the difference, R, in the reflectivitybetween the wafer to be processed and a reflectance value stored in thesource autocal file for a thermocouple or batch wafer. This value, R, issimilar in function to the correction constant of section 2. Using thesource autocal file with its reference backside reflectivity vaIuecorresponding to the backside of the wafer used to create the file thecomputer then uses the following equation (2) to adjust the autocal filefor the particular wafer that is about to be processed.

    Tnew.sub.i =T.sub.i +R*C.sub.i                             (2)

Where:

Tnew_(i) =new temperature value for the table in the ith position

T_(i) temperature value from the source autocal file in the ith position

R= the Correction Constant calculated from the difference between themeasured reflectance and the reflectance value contained in the sourceautocal file

C₁ =the Correction Coefficient corresponding to the ith position in theautocal table The correction coefficients, C₁ are the same that wereused in equation 1.

The newly calculated values are inserted in a third table. The thirdtable is a copied version of the second table in which the newlycalculated values for the particular wafer can be substituted.

Curve 98 in FIG. 3 represents a further refinement of curve 96 to adjustcurve 96 to take into account variations in a particular wafer to beprocessed. Curve 98 is approximated in the same manner as curve 96. Thatis, only one measurement is taken and the rest of the curve is predictedby reference to curve 96.

The ACE measurement works by measuring the backside reflectivity of eachwafer just before entry into the process chamber. The optics of thereflectometer chamber 10 are carefully designed so that the measurementsare made on the same location on the wafer as the pyrometer 36 in theprocessing chamber 30 will see. Therefore, any non-uniformity will notresult in emissivity errors.

The reflectometer chamber 10 is an additional piece of hardware whichmounts below the baseplate just to the left of the process chamber 30.As a wafer is held by transport arm 21 waiting to be loaded into thechamber, the system takes a reflectivity measurement. In this way thereis essentially no reduction in the throughput of the system. The changein reflectivity from wafer to wafer is directly related to the change inemissivity, even at room temperature. The emissivity changes arecalculated by the system computer. It is important to note that ACE doesnot measure emissivity, but only the small changes in emissivity fromwafer to wafer within a lot. Normal variations of 10° to 20° C. aretypical in some types of processes using standard closed looptemperature control. With ACE, the variations can be reduced to 1° to 2°C.

Although ACE is intended to compensate for small variations in backsideemissivity it can often do a good job correcting for larger changes aswell. One must be careful, however, because there may be somecombinations of backside conditions which could fool this system if itis used to correct for large changes in emissivity. It is better to usethe techniques discussed previously to make the gross emissivitycorrections and to use ACE to compensate for the smaller variationswithin a lot.

System Electronics

FIG. 4 is a block diagram of the electronics used to implement apreferred embodiment of the present invention. Computer 44 is connectedto various components of the system. First pyrometer 20, Iocated inreflection chamber 10, is connected to computer 44 through a firstanalog to digital converter 70. The output signaI of second pyrometer 36is fed through an isolation amplifier 72 and a second analog to digitalconverter 74 before being input to computer 44.

A second isolation amplifier 73 is preferably provided in parallel toamplifier 72, with amplifier 73 having a higher gain for the high-endcurves of FIG. 3. A switch 75, controlled by a line 77 from computer 44,allows quick switching between the two amplifiers, and thus between twogain levels. Alternately, a single amplifier could be used with a switchbetween two gain-setting resistors. However, this method could not beswitched as quickly.

In order to use an optical pyrometer to measure a wide temperature spansuch as 350° C. to 1300° C. it is necessary to adjust the gain of thedetector amplifier one or more times to obtain a measurable signal atlow temperatures while not saturating the signal at high temperatures.In a conventional optical pyrometer this is accomplished by a manualadjustment of the gain with a variable resistor. In this invention thepyrometer temperature span is achieved by the use of two fixed gainresistors in the detector amplifier circuit. Alternatively, we coulddefine the temperature resolution by using 3, 4 or a multitude of fixedgain resistors. The fixed gain resistors of the pyrometer amplifiercircuit can be switched mechanically using the machine's computercontrol to obtain ooverage of the entire temperature range. In thepreferred embodiment of the invention there are parallel amplifiercircuits to the pyrometer detector, each with a different fixed gain.Again, there can be two or more of these parallel circuits. Each circuitis connected to the computer through parallel input ports. The computerthen selects which input to read based on the temperature range ofinterest. This method is much faster since the computer can select aninput much faster than a mechanical relay can change a resistor.

An input 76 for connecting to the imbedded thermocouple 62 is located onprocessing chamber 30. Input 76 is connected to computer 44 throughthermocouple (TC) amplifier 78 and third analog to digital converter 80.

Lamp power source (LPS) 82 is connected to computer 44. LPS 82 bothtransmits a power level readout to, and receives a power level controlsignal from, computer 44 in order to control the processing of wafers inprocessing chamber 30.

A recorder output 84 is connected to computer 44 through first digitalto analog computer 86. Recorder output 84 is used to provide a hard copyof any of the tables or the process history for a particular wafer.

Computer 44 runs the calibration system using rapid reference software88. In the memory of computer 44 are stored the autocal tables 90containing the values from the tests performed upon various wafers. Inthe preferred embodiment there are three autocal tables. The firstcontains temperature, power level, and light emission values forthermocouple wafer 60 shown in FIG. 2. The second table containstemperature, power level, and light emission values for a batch wafer.The third autocal table contains temperature, power level, and lightemission values determined as a function of reflectivity for aparticular wafer to be processed.

FIG. 5 is a flowchart of the software used to control the computer formaking the temperature versus pyrometer output table in a preferredembodiment of the present invention. The lamp is first turned on (stepA) and the pyrometer output value (Pypoint) is zeroed (step B). A timeris then started (step C) to give enough time for one measurement to bedone. The pyrometer output is compared to a particular value beingmeasured (step D). If the pyrometer value is greater than the selectedpoint, the temperature is recorded (step E) and the next pyrometer pointis selected (step F). If the timer has not run (step G) and thepyrometer output is not at its maximum (step H), step D is repeated.Otherwise, if the timer has run, the power is incremented (step I) andthe timer is reset (step J) and the process is repeated Once the maximumpyrometer output has been reached, the lamp is turned off (step K) andthe procedure is completed.

In general, to those skilled in the art to which this invention relates,many changes in construction and widely differing embodiments andapplications of the present invention will suggest themselves withoutdeparting from its spirit and scope. For instance, a series of arc lampsor a conventional heating element could be used. The black body sourcecould be placed in the heating chamber so a single pyrometer could beused. An error factor could be figured in the equations rather thanstripping the top of the batch wafer. Thus, the disclosures anddescriptions herein are purely illustrative and are not intended to bein any sense limiting. The scope of the invention is set forth in theappended claims.

What is claimed is:
 1. An apparatus for calibrating a processing signalderived from characteristics of a semiconductor wafer, comprising:aprocessing chamber having a range of temperature settings includingmeans for holding a calibration wafer; temperature measurement meanscoupled to the processing chamber for transmitting a signal indicating atemperature of said calibration wafer at a particular temperaturesetting; light emission masurement means coupled to said processingchamber for measuring an amount of light emitted by said calibrationwafer at said particular temperature setting; and computer means forrecording the amount of light emitted and temperature of saidcalibration wafer connected to the temperature measurement and lightemission measurement means, including memory means for storing a firstcalibration table constructed from the measured light emission andtemperature values used to determine a level of the processing signal,the computer means being programmed to recall and modify entries of thefirst calibration table according to light emission values of a samplebatch wafer as measured by the light emission measurement means togenerate a second calibration table and further programmed to calibratesaid processing signal based on said entries of said second calibrationtable.
 2. The apparatus of claim 1 wherein said computer means isprogrammed to provide said calibrated processing signal as a controlsignal to a power supply for said processing chamber.
 3. The apparatusof claim 1 further comprising:light emission means for providing lightto be reflected off of the sample batch wafer and a batch wafer;reflection measurement means for measuring intensity of light reflectedoff of said sample batch wafer and said batch wafer and providing areflection signal to said computer means; and said computer means beingprogrammed to modify said second calibration table in accordance with adifference in said reflection signal for said sample batch wafer andsaid batch wafer to generate a third calibration table.
 4. The apparatusof claim 3 wherein said light emission means and said reflectionmeasurement means are external to said processing chamber and furthercomprising a transfer arm for loading a particular wafer into saidprocessing chamber and passing said particular wafer over said lightemission means and reflection measurement means.
 5. The apparatus ofclaim 3 wherein said light emission measurement means and saidreflection means are infrared pyrometers.
 6. An apparatus forcalibrating a processing signal derived from characteristics of asemiconductor wafer, comprising:a processing chamber having a range oftemperature settings including means for holding a calibration wafer;temperature measurement means coupled to the processing chamber fortransmitting a signal indicating the temperature of said calibrationwafer; light emission measurement means coupled to said processingchamber for measuring an amount of light emitted by said calibrationwafer; light emission means for providing light to be reflected off of asample batch wafer and said calibration wafer; reflection measurementmeans for measuring the intensity of said light reflected off of saidsample batch wafer and said calibration wafer and providing a reflectionsignal; and computer means for recording the amount of light emitted andtemperature of said calibration wafer connected to the temperaturemeasurement and light emission measurement means, including memory meansfor storing a first calibration table constructed from measured lightemission and temperature values used to determine a level of theprocessing signal, the computer means being programmed to recall andmodify the first calibration table in accordance with a difference insaid reflection signal for said sample batch and calibration wafer togenerate a second calibration table and to calibrate said processingsignal based on said entries of said second calibration table.
 7. Anapparatus for calibrating a processing signal derived fromcharacteristics of a semiconductor wafer, comprising:a processingchamber including means for holding said wafer; a long arc lamp forheating said processing chamber to a range of temperature; a powersupply for said long arc lamp; temperature measurement means coupled tothe processing chamber for transmitting a signal from a thermocoupleattached to a calibration wafer for indicating the temperature of thecalibration wafer; a first infrared pyrometer coupled to said processingchamber for measuring an amount of light emitted by the calibrationwafer; light emission means mounted outside said processing chamber forproviding infrared light to be reflected off a particular wafer; asecond infrared pyrometer mounted outside said processing chamber formeasuring the intensity of said light reflected off of said particularwafer and providing a reflection signal; a transfer arm for loading saidparticular wafer into said processing chamber and passing saidparticular wafer over said light emission means and said second infraredpyrometer; and computer means for recording the amount of light emittedand temperature of the calibration wafer connected to the temperaturemeasurement and light emission measurement means, including memory meansfor storing a first calibration table constructed from the measuredlight emission and temperature values used to determine a level of theprocessing signal, the computer means being programmed to recall andmodify entries of said first calibration table according to lightemission values of a sample batch wafer as measured by the firstpyrometer to generate a second calibration table, said computer meansbeing programmed to modify a light emission value from said secondpyrometer with said second calibration table and to provide a modifiedsignal as a control signal to said power supply for said processingchamber, said computer means also being programmed to modify said secondcalibration table in accordance with a difference in said reflectionsignal between a batch wafer and one of said sample batch andcalibration wafers to generate a third calibration table and tocalibrate said processing signal based on said entries of said thirdcalibration table.